There are many devices intended to provide physical placement and manipulation of objects along and around multiple axes. Often, mechanical, optical, electronic, genetic, medical, and chemical disciplines require exact placement of various components combined with an ability to manipulate in one or more dimensions. Possibly one of the more prominent needs is in the optical world of precision lasers, lenses, and fiber optics. Accuracies are often called out in subwavelength dimensions and will go into the subatomic region in the future, such as for scanning tunneling microscopes (STM) and atomic force microscopes (AFM).
Conventional methods include a series of adjustable leadscrews which are attached to a working platform or table at one end and some suitable base on the other. Each axis may then be manipulated by turning a micrometer type positioner a prescribed amount which, in suitable base on the other. Each axis may then be manipulated by turning a micrometer type positioner a prescribed amount which, in turn, moves the working platform or table to the desired position relative to its base or some other reference such as an optical axis.
Many commercially available positioners require that the item to be positioned (e.g., lens, mirror) be mounted within the confines of a relatively small area, usually a circle, in the central portion of the positioner. Others call for cantilevered positioning of the item to be positioned. Both of these conditions have large potential for limiting the usefulness of the positioner.
In the first case mentioned above, versatility is limited due to the physical limitation placed on the size of item to be positioned. One is required to have several different positioners with differing sized working diameters to satisfy differing needs because of size differences of objects to be positioned.
Loads that are placed on a positioner in a cantilevered position can cause bending stresses on elements of the positioner. The torque may result in flexing or bending with an undesirable deflection which may give rise to cross-coupling. Cross-coupling is a phenomenon wherein adjustment of one parameter (in one degree of freedom) disturbs a setting in another parameter. For example, changing position along the principal X-axis may also change position along the Y-axis or the Z-axis, and the unwanted change may not be immediately apparent to the user.
As requirements for positioning become more stringent, cross-coupling becomes more of a problem, because movement that might previously have been acceptable is no longer acceptable because of the more stringent requirements. Trends in design have been to more complicated and therefore more expensive micropositioners.
If cross-coupling is going to be a problem, and readjustment will be needed in any case, then a viable approach would be to eliminate guides, bearings, and pivots to the greatest degree possible, providing maximum accuracy, stability, and versatility with a minimum of sophistication, accepting a certain amount of cross-coupling as a consequence, and committing to the readjustment that cross-coupling demands. Moreover, there are many applications where cross-coupling is not as serious as in some other applications.
What is clearly needed is a micropositioner which overcomes the problems of load centering and allows for different sizes and shapes of objects without giving up other needed characteristics such as resolution, repeatability, travel range, and overall desired accuracy. The new positioner should minimize complexity and parts to reduce manufacturing cost. Such a positioner would allow one versatile piece of equipment to take the place of several devices at a reduced cost.